全文获取类型
收费全文 | 1561篇 |
免费 | 58篇 |
国内免费 | 3篇 |
专业分类
化学 | 1216篇 |
晶体学 | 27篇 |
力学 | 43篇 |
数学 | 78篇 |
物理学 | 258篇 |
出版年
2023年 | 9篇 |
2021年 | 12篇 |
2020年 | 21篇 |
2019年 | 28篇 |
2018年 | 15篇 |
2017年 | 13篇 |
2016年 | 29篇 |
2015年 | 35篇 |
2014年 | 34篇 |
2013年 | 84篇 |
2012年 | 80篇 |
2011年 | 84篇 |
2010年 | 55篇 |
2009年 | 49篇 |
2008年 | 84篇 |
2007年 | 94篇 |
2006年 | 98篇 |
2005年 | 79篇 |
2004年 | 76篇 |
2003年 | 74篇 |
2002年 | 61篇 |
2001年 | 26篇 |
2000年 | 39篇 |
1999年 | 18篇 |
1998年 | 19篇 |
1997年 | 18篇 |
1996年 | 13篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 18篇 |
1977年 | 19篇 |
1976年 | 14篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 5篇 |
1972年 | 5篇 |
排序方式: 共有1622条查询结果,搜索用时 31 毫秒
141.
A new synthetic approach to quinazolines bearing a carboxy group is described. Reaction of 5-carbonyl substituted 1,3,6-tri-methyluracils (I) with dimethyl acetylenedicarboxylate or electron-deficient olefines affords quinazoline derivatives (III-VI) pyrimidine(Z)-dienols (II) formed by base-catalyzed isomerization. 相似文献
142.
143.
144.
Calorimetric measurements at 25°C were made to determine the thermodynamic quantities for the intercalation of pyridine with α- and γ-zirconium phosphates. These phosphates showed exothermic reactions with ΔH0 = ?59.3 and ?21.9 kJ mole?1, respectively. The large difference between the depyridination temperatures for both intercalates is rediscussed with the aid of the ΔG0 data obtained. 相似文献
145.
H. Suematsu K. Ohmatsu K. Sugiyama T. Sakakibara M. Motokawa M. Date 《Solid State Communications》1981,40(3):241-243
The whole magnetization curve of the first stage compound C6Eu has been measured by using pulsed fields up to 400 kG below 40 K. For H ⊥ c, c being the crystal c-axis, four regions are observed in the magnetization curve; I) the initial magnetization region with an apparent moment of ~ 0.6microB per Eu ion (H < 12 kG), II) the intermediate region with nearly constant moment of 2.2 – 2.7 microB, which corresponds to the full moment of Eu2+ ion (22 < H < 82 kG), III) the region of a linear field dependence (82 < H < 205 kG), and IV) the saturation region above 205 kG, where the saturation moment is found as 6.2 microB. For H//c, the magnetization increases monotonically and approaches to a saturation value corresponding to 6 microB above 240 kG. 相似文献
146.
To explore the structure-dependent hydrogen abstraction in antiparallel and parallel G-quartet DNA structures, the photochemical reactivity of 5-iodouracil ((I)U)-containing human telomeric DNA 22-mers was investigated under the 302 nm UV irradiation conditions. We discovered that only antiparallel ODN 4, in which the second T residue in the diagonal loop of the antiparallel G-quartet is substituted with (I)U, was rapidly consumed as compared with parallel ODN 4 and the other (I)U-containing 22-mers under the irradiation conditions. Product analysis of the photolyzate of antiparallel ODN 4 indicated that a 2'-deoxyribonolactone residue was effectively produced at the 5' side of the (I)U residue in the diagonal loop. Photochemical 2'-deoxyribonolactone formation was also found in the (I)U-containing diagonal loop of antiparallel G-quartets d(GGGGTTT(I)UGGGG)(2) and d(GGGGTT(I)UTGGGG)(2), whereas the reaction did not occur at other DNA structures, including the single-stranded form, the loop region of the hairpin, and linear four-stranded G-quartets. The results clearly indicate that this type of 2'-deoxyribonolactone formation efficiently occurrs only in the diagonal loop of the antiparallel G-quartet. Furthermore, we found that 2'-deoxyribonolactone was formed at the (I)U-containing G-rich sequence of the IgG switch regions and the 5' termini of the Rb gene, suggesting the formation of an antiparallel G-quartet with a diagonal loop in these sequences. These results suggest that the present photochemical method can be used as a specific probe for the antiparallel G-quartet with the diagonal loop. 相似文献
147.
Acceleration waves propagating in isotropic solids at finite temperatures are studied by applying the method of singular surfaces to a new continuum model derived statistical-mechanically from a three-dimensional lattice model. The continuum model explicitly takes into account the microscopic thermal vibrations of the constituent atoms as one of the field variables. The propagation speeds and the ratios of mechanical and thermal amplitudes for both longitudinal and transverse waves are consistently determined. The differential equations that govern the time variation of the amplitudes of the waves are also derived. The analytical results, which are valid over a wide temperature range that includes the melting point, are evaluated numerically for several materials, and their physical implications are discussed. One of the findings to be emphasized is that of the singularities of the characteristic quantities at the melting point.Received: 13 March 2003, Accepted: 20 June 2003PACS:
62.30. + d, 65.40.-bM. Sugiyama: Correspondence to
Dedicated to Prof. Ingo Müller on the occasion of his 65th birthday. 相似文献
148.
149.
4,4'-Dihydroxytriphenylmethanes were synthesized using Br?nsted acid or Lewis acid in yields of 24-86% as target compounds for developing antiviral agents. Most of the 4,4'-dihydroxytriphenylmethanes showed significant activity against herpes simplex virus type 1 (anti-HSV-1 activity) in a plaque reduction assay. Higher cytotoxicity was observed generally in halogenated 4,4'-dihydroxytriphenylmethanes (2a-d) than in non-halogenated derivatives. The non-halogenated derivative, 4,4',4"-trihydroxy-3"-methoxytriphenylmethane (3), showed remarkable antiviral activity with an EC(50) value of 1.8 microg/ml. 相似文献
150.
Ohki Y Sunada Y Honda M Katada M Tatsumi K 《Journal of the American Chemical Society》2003,125(14):4052-4053
The [8Fe-7S] core of the P-clusters in nitrogenases is unique among the known [Fe-S] clusters which are essential to electron-transfer processes in nature. The [8Fe-7S] cluster has been thought unstable and to exist only in protein environments. We found that this unusual [8Fe-7S] structure can be self-assembled from the reaction of Fe(II) bis-amide, tetramethylthiourea, 2,4,6-triisopropylbenzenethiol, and elemental sulfur in a specific mole ratio. The structure of the complex isolated therefrom closely resembles that of the reduced form (PN) of the P-clusters, while the 6Fe(II)2Fe(III) oxidation state was manifested by the M?ssbauer study. 相似文献